At the moment I encountered 2 way of reproducing this bug.
1) First if all, you need to be wounded (e.g.: player setdamage 0.5;), or shoot the other player / AI
2a): If you press the "step over" button right after (almost at the same time) the healing animation starts (you may need to move to do this) and triggers the bug.
2b): Reloading can also cause this, if you hit it the reload just before the healing animation ends. If the reload animation ends before the healing animation ends, the bug does not trigger.